1. Field of the Invention
The present invention relates to recording heads for ink mosaic printers, and in particular to such recording heads having a plurality of channels for ejecting the recording liquid toward a carrier medium operated by an electro-mechanical transducer.
2. Description of the Prior Art
Ink mosaic recorders having recording heads are known in the art in which a number of recording channels communicate between an ink supply and a nozzle or other termination of the channel from which the ink is ejected toward a carrier medium. The ink may be ejected from the channels in the form of individual ink droplets by the selected operation of individual transducer elements surrounding the channels, such as piezoelectric elements which when operated by application of suitable electronic pulses bring about a change in pressure in the respective channel by means of contraction and expansion of the element. A recording head of this type is disclosed in German OS No. 25 43 451, corresponding to U.S. Pat. No. 4,158,847. The recording head disclosed therein may contain, for example, twelve channels having twelve openings which form two parallel rows each containing six nozzles. A recording head of this type enables the recording of arbitrary characters within a 12.times.9 array on a data carrier.
For the practical use of an ink mosaic recorder it is not only necessary to insure operation which meets the technical requirements, but also a good recording quality must be achieved. The latter consideration presents several problems if the mosaic recording process involves the formation of individual characters by droplets of recording liquid applied in punctiform manner to a recording medium, such as paper. Thus, for example, it must be insured that the droplets of ink applied to the paper dry sufficiently rapidly to avoid smearing of the text. If an ink is used which penetrates rapidly into the fibers of the paper, even if the ink drying time is minimal, the ink will be visible on the reverse side of the paper. In order to avoid this latter disadvantage, it is known to use an ink and paper combination which together limit the flow properties of the ink once applied to the paper. This attempted solution has the disadvantage, however, that the expansion of the ink droplets sprayed onto the paper is reduced to such an extent that the punctiform arrangement of the individual characters become apparent and the overall text loses the appearance of continuity for the reason that the individual ink droplets forming the character no longer overlap sufficiently.
Proposed solutions to counteract these effects, such as increasing the size of the ejected ink droplets or utilizing a narrower distribution of the recording nozzles, all involve a substantial mechanical outlay and contribute to an increasingly complex recording head. For example, an increase in the size of the ink droplets results in greater ink consumption, a longer drying period, a higher impact sensitivity of the nozzles, and, as a result of the formation of so-called "satellite" droplets, to a poorer formation of droplets. Narrowing the distribution of the recording nozzles necessitates a larger number of channels inside the recording head and leads to increased production cost.